Resulting from calculation, rope design, material, manufacturing
It is well known that great differences in fatigue bending cycles ( 1:15 and greater) may be achieved with the same rope construction (rope characteristics), tested on the same fatigue bending machine (application), with the same test parameters but manufactured by different rope manufacturers (VDI 2358). Field results also show big differences but here only under consistent working condition can the real rope quality be judged. Also, quite often other rope damages than fatigue, are the reason for the necessity to discard the rope. The reason must be "different" rope quality by different manufacturers. Why do we have these great differences? There are many influences relating to the rope design, core diameter relation (Müller/Greis, 1979), lay length and lay angle relation, contact angles, additionally, the type of core can be critical. It seems that in 8 strand constructions a 6 strand core is not as sensitive as a 8x7+1x19 construction. This type of core shows more internal centre strand or core breaks than the 6 strand core. There are also differences from one rope production length to another. Here the "consistency" i.e. reproduction of wire rope in all details must be the reason. Here the consistency (reproducibility) is the key factor. One way is manufacturing by craftsmanship, the other industrialized manufacturing by giving all machine and tool setting data within tolerances. These values will be controlled by supervision. Traditionally, as is usual in old crafts, e.g. 170 years of wire rope- supervisors set the machines and tools using their experience. Today's quality requirements ask that one rope is manufactured like the other. Therefore supervision has to make sure that all pre-given data are kept within the given tolerances. If Supervisors still set the machine and tool data, the rope quality cannot be consistent. Therefore in new industrialized production, each possible setting value must be given to the operator on the production papers job cards). When supervisors set the machine and tool data by their experience machine efficiency will also be reduced, because experimenting until the requested results have been achieved, takes time. There are not too many wire rope companies in the world manufacturing to the "set data" method. Roebling (some time ago, one of the most famous wire rope companies) has shown already in 1935 by giving the values for setting the preform head that this is possible (Roebling, 1935). Some rope manufactures still question whether the setting values can always be the same; with the argument, that wire stresses are always different. The new EN Standard for wire ropes (EN Type of ropes, rope construction, designation, classification etc.) could have helped to give new impetus for the wire rope industry. For the first time the same terminology would have helped to understand presentations. lt is a pity, that EN has not followed the first draft using a systematic, easy to understand system. Now English abbreviation (but using the English words e.g. Natural Fibre Core NFC) without a system have been introduced. This is hard to understand and learn for people speaking other languages.
Author(s): Voigt, P-G.